Next time you're watching Jurassic Park and a T. rex roars, remember that what you're hearing could include the call of a male koala—along with the seemingly more appropriate sounds of tigers and elephants. In fact, the koala's bellow would make more sense coming from an elephant: The deep, gravelly noise is 20 times lower than it should be considering the marsupial's size.

How does this disarming creature manage such vocal depth? The answer is a newly discovered vocal organ—essentially a second set of vocal folds outside of the koala's larynx—discovered by researchers at the University of Sussex.

These extra vocal folds, called the "velar vocal folds" in a study published Monday by the journal Current Biology, are more than three times longer and roughly 700 times heavier than the vocal folds previously discovered on the koala's larynx.

"Larger structures can oscillate at lower frequencies," Benjamin D. Charlton, the researcher who led the study, told BBC News. "Just think of a guitar string—as you shorten the string by placing a finger on the fret board, you raise the frequency of the sound produced, and the thickest strings produce the lowest frequencies."

For male koalas, the velar vocal folds are crucial, as female koalas are attracted to a deep voice.

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